There is interest in utilizing synthetic polymer particles as reinforcement in tire rubber compounds in place of traditional fillers, such as carbon black and silica. Such synthetic fillers may include nylon, polyaramid, syndiotactic polybutadiene, and various block copolymers. There are at least two problems generic to all of these approaches. First, the Tg of the reinforcing polymer particles has to be high enough so that the particles do not soften at the operating temperature of the tires (Tg>110-120° C.). At the same time, the melting temperature should be low enough so the particles melt during mixing (Tm<170° C.), or the particles be made of small enough particle size. Second, the cost of most of these reinforcing materials is too high.
1,1-Diphenylethylene (DPE) is a monomer that does not homopolymerize due to steric hindrance from the two aromatic rings, but that can copolymerize with styrene by anionic polymerization in an almost ideal fashion (see e.g., Yuki et. al., B. Chem. Soc. Jpn. 1967, 40, 2659-2663; Xu et al., Macromolecules 2003, 36, 5432-5434.)
The copolymer Tg accordingly can be varied between 100° C. (100% polystyrene) and about 168° C. (50 mol % DPE). The copolymerization of DPE with other monomers, such as butadiene and isoprene, by anionic polymerization has also been studied (Quirk et al., Macromol. Chem. Phys. 2003, 204, 1719-1737.) Block copolymers, with a soft segment (PBd) and a hard segment (PS-co-DPE) were also synthesized (Knoll et al., Ionic Polymerizations and Related Processes. Puskas et al., ed., Kluwer Academic Publishers, Netherlands, 1999, p 219-221; Gausepohl et. al. Des. Monomers Polym. 2000, 3(3), 299-315.) Nevertheless, the previous work was directed towards making an improved styrene copolymer, for applications in HIPS, ABS, etc. Use of such a copolymer in tires is unknown.